A standard blood-collection system such as described in German patents 2,948,653 and 3,049,503 of W. Sarstedt comprises a double-pointed needle and a generally tubular holder into whose front end a collar mounted on the needle between its points can be mounted so that the front end of the needle projects from the front end of the holder and the rear end of the needle projects back into the holder. A blood-collection vial with a pierceable cap can fit inside the holder. Thus to draw blood the front end of the needle is poked into a vein so that flow through the needle is established, possible by use of a syringe temporarily connected to the needle. Then the needle, while still in the vein, is fitted to the holder and a collection vial is pressed into the rear end of the holder so that the rear end of the needle pierces its cap and blood can flow into the vial. Several such vials can be filled this way, as is necessary for performing complex blood work.
Once the necessary amount of blood is drawn and the filled vials have been set aside, the needle is pulled out of the vein and normally must be capped in accordance with procedures described, for instance in "Special Report and Product Review" (Health Devices, p. 169ff, May 1991, vol 20, no. 5). In some situations the tubular holder can be reused and it is known to provide a separate large casing into which the entire needle assembly can be fitted when it is no longer needed. Either way it is absolutely essential to avoid needlesticks so that both ends of the needle itself have to be capped for disposal. Such capping is a problem and presents in itself a chance of needlestick to a technician who does not accurately fit the needle to the protective cap, normally the one it is delivered with. The classic needlestick accident is for the technician to stick the needle into the hand holding the protective cap it is being fitted to.
Other syringe systems are known from European patents 0,430,159 of J. Odenthal and 0,602,882 of J. Bell as well as from German Utility Model 91 09 584 assigned to U. Demuth which have a piston specially constructed that it can be coupled to the rear end of the needle assembly. Thus once the injection is complete, the piston is pushed fully forward and normally twisted to couple it to the needle, then the piston is pulled back to retract the needle into the body of the syringe, where it is protected. Such a system is usable for injections since the syringe is essentially empty when the injection is completed so that the piston is fully forward where it can be coupled to the rear end of the needle collar. In a blood-collection system, however, the vial is full and often does not even have a piston, so that this system is not usable.